Risk, raw feeding, and pathogens: a review

Some of the issues I'd like to discuss are assessing the potential risk of to the dogs, assessing the risk to humans who are around raw-fed dogs, and the general issue of how to evaluate risks. References are in parentheses, and a list of sources can be found at the end of this article, with short excerpts and web links to full-text or author's abstracts in most cases.

RISKS TO DOGS

First, the issue of risk in feeding a raw diet is not simple. ALL foods have some degree of risk, so the question isn't whether risk exists. The question is whether the risk is unacceptable.

You may think you want zero risk - but that's not a choice you get in life, because all foods carry some type of risk.

Raw meat can indeed be contaminated with e. coli 0157, camphylobacter, or other pathogens.

However, kibble can also contain disease-causing mold and other pathogens. Studies by Bueno (2001), Gunsen (2002), and Maia (2002) found aflatoxin, a toxic mold, in pet food samples. Aflatoxin contamination of dog kibble resulted in approximately 25 dog deaths in 1998 (Texas) and vomitoxin was found in batches of Nature's Recipe kibble in 1995 (Food and Drug Administration, 1995). At least seven dogs have died from unknown contamination of Petcurean pet food, recalled by the manufacturer in October 2003 (Syufy, 2003).

Bacteria and mold are not the only risks involved in choosing a food for your pet. For example, there is some research that says that small particle size of food is a risk factor in bloat, so with regard to bloat, feeding large meaty bones would be less risky than feeding any kibble (Theyse, 1998). Even the packaging of commercial food can carry some risk, as one study of canned pet foods showed that Bisphenol A, an industrial chemical and suspected endocrine disruptor leached from the cans into the food (Kang, 2002).

Dogs are more resistant to most of the common raw meat pathogens than are humans. (Consider the fact that many dogs use the kitty litter box as a snack tray without ill effects. Does anyone really want to argue that cat feces are free of pathogens?) Dogs are resistant - NOT immune - from the disease potential of these pathogens, and healthy dogs can harbor them without symptoms. Beutin (1993) found verotoxin producing e. coli in 4.8% of apparently healthy dogs and Dahlinger (1997) cultured various types of bacteria, including some forms of e. coli and salmonella from the lymph nodes of 52% of apparently healthy dogs brought in for elective spays. Most dogs can eat clean raw meat without a problem, even if the same raw meat would make humans very sick.

Still, a dog with a compromised immune system or digestive system is going to be more at risk for illness from any infectious agent than a dog who is healthy. So I would be reluctant to feed raw meat to an ill dog, a very young puppy, or a very elderly dog who has not previously been fed a raw diet.

I recently posted a article to the VETMED list about KSU's studies on Alabama Rot (a/k/a hemolytic uremic syndrome) in Greyhounds fed raw meat. (Greyhounds, 1995) Some people immediately posted "atta girl" posts to me privately. While I have no doubts about the accuracy of the KSU research, I think most of the readers of VETMED are unaware of exactly what kind of raw meat is fed to racing greyhounds.

Racing greyhounds are routinely fed raw "4-D meat" as part of their diet. 4-D meat is unfit for human consumption because the source of it is animals that died of natural causes (not via normal slaughter procedures) and includes animals which were diseased, or dying when they went into the slaughterhouse. This is meat which has either not been inspected by the USDA or it failed the inspection. This is not the quality of meat most pet owners buy if they are feeding their pets raw meat. 4-D meat is very foul stuff, and has the potential to contain much more in the way of pathogens than the meat that you buy in the supermarket. I would never feed a dog raw 4-D meat.

I don't know of any published veterinary reports of Alabama Rot in pet dogs fed raw diets from USDA-inspected meat. It is, unfortunately, mainly a problem caused specifically by the feeding of unwholesome raw 4-D meat - not raw meat generally.

So, my personal opinion is that with regard to the dog's health, feeding USDA graded raw meat to dogs is a reasonable choice for some owners to make as long as precautions are taken to avoid excess risk (for example, don't let the meat sit around at room temperature before giving it to the dog.)

RISK TO HUMANS

Studies of pet dogs have shown e. coli O157 and salmonella in the feces of pet dogs - but most of these studies were not limited to dogs fed raw diets. So, kibble fed dogs and dogs fed rawhides, pig ears, and chew hooves also carry this risk.

However, before getting too fixated on dogs as a source of pathogens for humans, consider that the most notorious cases of food poisoning have been caused by poor hygiene from human sources - such as cooks and farmers.

While undercooked and raw meat is sometimes implicated in food poisoning cases, there have been an enormous number of cases of salmonella and e. coli from fruits and vegetables. The seemingly innocuous bean sprout has been linked to many outbreaks of food poisoning, as have melons, salads, and apple cider (Health Canada, 2002, and USDA 1995.) In other words, while raw meat is a a risk, so is almost ANY uncooked food that you eat. There has been one salmonella outbreak linked to almonds. (Chan et al. 2002)

So, are people at additional risk of getting pathogens from coming in contact with a dog fed raw meat? There isn't a lot of research that is directly on topic for this. There are studies of raw-fed dogs (Joffe and Schlesinger, 2002) but these do not carefully compare the raw fed dogs to a similar population fed commercial dog food. (See the commentary on Joffe's study by New n.d.).

I have seen studies of pet dogs that show that food-borne pathogens were present in a surprisingly large proportion of the dogs tested. Hackett and Lappin (2003) found infectious agents in the feces of 26% of healthy Colorado dogs. As far as I can tell, this study was NOT limited to dogs eating raw diets. Fukata et al (2002) found salmonella antibodies in 15% of apparently healthy dogs.

I think that you can reduce any potential risk of food poisoning related to dogs by simply having good hygiene - scrupulously washing your hands after cleaning up after your dog and washing up thoroughly before eating. Keeping the dog itself clean probably doesn't hurt, either. And it would make sense to avoid letting your dog lick you right after eating a chicken neck.
For these reasons, I think that someone with pets and toddlers might want to avoid raw diets because small children will not follow the above rules. Kids often will let the dog lick their face any old time, and they may even try to taste the dog's meals. (Sato et al. 2000.)

RISK ASSESSMENT

Aside from the concept of 'relative risk' there is the question of risk versus benefit. If people were completely happy with the health of dogs from kibble feeding, the entire "raw foods" movement would have never taken root. There's nothing more convenient than pouring kibble into a dish. So some people must be seeing a benefit from feeding raw.

I think that most veterinarians' assessment of risk from raw diets is skewed by the fact that normal, healthy dogs are not generally seen by vets, and that most nutrition research is done using commercial diets. If there is a large population of totally healthy dogs eating raw diets, they may never be noticed by a veterinarian. On the other hand, vets will usually see the dogs who got the 3-day old chicken bones from the garbage can, or the one whose owner misguidedly thought it was a good idea to give their dog the skin and bones from their holiday turkey.

Raw diets do carry risk. These can be reduced by feeding the freshest cleanest meat the owner can buy and following all the rules about temperature, storage and hygiene (FSIS, 1999).

Kibble diets and dog treats also carry risk - and these can be reduced by buying fresh and high-quality food, rather than the cheapest stuff available, and by following proper storage and hygiene rules. But it's worth noting that some of the priciest brands of kibble were recalled because of toxic contamination, so a high price does not ensure safety.

I don't think there is one right way to feed dogs. I think that careful attention to nutrition and hygiene reduce the risk associated with whatever feeding regimen you choose. It's interesting to note that feeding raw meat is intensely controversial, while feeding pig ears and jerky - which carry similar if not higher risks for contamination - is widely accepted as reasonably safe.

Incidentally, in case anyone is wondering, the main diet for my dogs is free-fed kibble. I free feed because it helps prevent gluttony, and I have never had a case of bloat in Greyhounds, which are a somewhat bloat-prone breed. I also routinely feed my dogs raw chicken parts. I feed bony chicken parts because I have found this to be the most effective way of keeping my dogs' teeth clean. I haven't noticed any other big change in their health, but they love the chicken parts and their teeth are clean and their breath sweet as a result. Greyhounds are notorious for foul teeth as they age, but even my oldest dog has remarkably clean teeth.

With regard to the risk, I can only share my experience, in that I've not seen any illnesses in the dogs I can attribute to the raw meat nor to the kibble. I made my choice because I know of more pet greyhounds that have died from the anesthesia involved in teeth cleaning and other elective surgeries than have died from eating a raw diet.

I wrote this article to seriously examine the question a VETMED subscriber asked about the potential for risk when using raw-fed dogs as therapy dogs. As long as the dogs aren't fed raw meat during therapy sessions, I don't see a problem. While these dogs may carry pathogens, so may dogs fed kibble or pig ears, or rawhide. One survey found salmonella contamination of 41% of the dog treats examined (White et al, 2003). Accordingly, it would be not be logical or fair to bar raw fed dogs from a therapy dog program, unless you are also barring all dogs who are fed pig ears, rawhides, and other similar treats.

"This article reports on the identification of mycoflora of 21 dry pet foods (12 belonging to dogs and 9 to cats) that corresponded to 8 commercial brands [...] Some genera and species isolated and identified from the foods analyzed are potentially producing toxins, which are known as mycotoxins. This involves a risk for animal health."

"Treat Makers, L.L.C., a manufacturer of natural pet treats, is voluntarily recalling Medalist brand pig ear pet treats, lot numbers 07600EXU3 and 08300EXU1, due to possible contamination with Salmonella. Pet owners can become ill by touching their mouth or food without washing their hands after handling the pet treats."

"The Food and Drug Administration today issued a nationwide public health warning alerting consumers about a number of recent cases in Canada of human illnesses apparently related to contact with dog chew products made from pork or beef-derived materials (e.g., pigs ears, beef jerky treats, smoked hooves, pigs skins, etc.). [...] Initial reports of illnesses came from Canada and involved Canadian products, but subsequent examination of similar products produced in the U.S. indicate that all pet chew products of this type may pose a risk."

"Aflatoxin levels were determined by ELISA in 18 dog and 20 horse feed samples, collected from different firms from June 2000 to June 2001 in Turkey. The minimum and maximum levels of total aflatoxin in the dog and horse feeds were <1.75-20 microg/kg and <1.75-14 microg/kg, respectively; 3/18 dog feed samples (16.7%) and 2/20 horse feed samples (10%) exceeded the Turkish tolerance limit of 10 microg/kg in food or feed."

"Worldwide between 1995 to 2001, there have been 13 outbreaks of foodborne illnesses linked to sprouts. In most instances, the illnesses were caused by either Escherichia coli (E. coli) O157:H7 or Salmonella bacteria."
"Anyone who eats raw sprouts is at risk for exposure to E. coli O157:H7 or Salmonella bacteria. However, the risk of serious health effects is greater for young children, seniors, and people with weak immune systems."

"In August 1999, the province of Alberta reported an increase in Salmonella Infantis cases. The initial investigation conducted by the regional public-health authority of Calgary, Alberta, demonstrated that eight of 12 S. Infantis cases were dog owners, and that nine of 12 had had exposure to pig ear dog treats."

"Salmonella was isolated from 80% of the BARF diet samples (P < 0.001) and from 30% of the stool samples from dogs fed the diet (P = 0.105). Dogs fed raw chicken may therefore be a source of environmental contamination."

"Doane Products Company announced today a recall of dry dog food produced between July 1 and August 31, 1998, at its Temple, Texas plant. [...] Doane officials said a veterinary diagnostic laboratory has attributed the deaths of approximately 25 dogs to aflatoxins. Aflatoxins result from a naturally occurring mold which at high levels can cause liver damage. The mold may be more likely to occur in corn that has been subjected to extreme weather conditions."

"A total of 158 dog treats derived from pig ears and other animal parts were randomly collected nationwide and assayed for the presence of Salmonella. [...] Forty-one percent (65/158) of samples were positive for Salmonella. [...] CONCLUSIONS: The study indicates that animal-derived dog treats in the USA could be a potential source of animal and human infections with Salmonella, including multidrug-resistant Salmonella strains."

Copyright 2003, Stacy Pober. All rights reserved.
Contact the author.The above article originally appeared on the VETMED discussion list in November 2003.
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